The subject matter disclosed herein relates to an X-ray CT (Computed Tomography) apparatus and an X-ray CT imaging method, and particularly to an X-ray CT apparatus or method for conducting imaging using X-rays with a plurality of X-ray tube voltages.
For X-ray CT apparatuses representative of those having a two-dimensional X-ray area detector of a matrix structure, exemplified by a multi-row X-ray detector or flat-panel detector, there have been techniques called dual-energy imaging (or Dual Energy Scan) that produces an image representing a difference of dependency of the X-ray absorption coefficient upon the X-ray tube voltage using tomographic images at a plurality of X-ray tube voltages (e.g., see Japanese Patent Application Laid Open No. 2006-6531).
More specifically stated, in such dual-energy imaging, an X-ray tube generates first X-rays with a first X-ray tube voltage and second X-rays with a second X-ray tube voltage, those voltages being representative of the plurality of X-ray tube voltages, and a data collecting apparatus collects X-ray projection data separately at the plurality of X-ray tube voltages. Based on the X-ray projection data at the first X-ray tube voltage and those at the second X-ray tube voltage, a difference in dependency of the X-ray absorption coefficients upon the X-ray tube voltage between the first and second X-ray tube voltages is represented as an image. By the method, an equivalent image of a certain material can be obtained as an image by dual-energy imaging, in which image a contrast is given between a plurality of different materials that would otherwise be indiscernible in the resulting image because of close CT values if imaging was conducted with a constant X-ray tube voltage.